EP0082321B1 - Flexible fibre-reinforced plastic spring and press for its manufacture - Google Patents

Description

The invention relates to a spiral spring according to the preamble of claim 1 and its manufacture.

In such a spiral spring known from DE-C-1 231 967, the spring thickness changes are achieved by a corresponding fiber structure of the spacer layer. For this purpose, the fibers of the spacer layer do not necessarily have to be unidirectionally oriented, but can also have a haphazard orientation, corresponding to the spiral spring known from EP-A-5 916. Finally, according to FR-A-1 411 011, the functional purpose of the spacer layer, to ensure equal spring tensions in the spring cover layers over the entire length of the spring, is also achieved by using fiber tissue.

For all known embodiments of the spiral spring, regardless of the fiber structure and the shape of the spacer layer, there is the problem in the middle of the force application of force without weakening the fiber strands of the cover layers through holes, provided that these can only be created in the finished spring base body, for example for reasons of production simplification . This is not just about preventing feather breaks par excellence. Rather, such bores that penetrate the cover layers and usually sit on the longitudinal edges of the spring favor fiber damage, which lead to a gradually progressive reduction in bending strength at the relevant points that are subject to maximum stress during spring deflection with simultaneous torsion. This problem cannot be solved with the (naturally) existing demand for the greatest possible connection security by a fitting that is merely jammed with the spiral spring.

The invention is therefore based on the object, in the case of a spiral spring of the type mentioned, to be able to introduce bores for the application of force only in the finished spring base body without reducing the strength of the cover layers; moreover, a device which simplifies the production of such a spiral spring is to be shown.

The first part of this task is solved according to the characterizing part of patent claim 1, i.e. by a possibility of restricting spring connection bores to the spacer layer while structuring the same in such a way that these bores have a much less strength-reducing effect than with unidirectional fiber structures or structures deviating therefrom without a specific fiber orientation . This is because the proposed crosswise fiber orientation allows the spacer layer to be stressed by both the longitudinal and transverse forces. In this way, the perforation reveal pressures that occur can be optimally absorbed by the spacer layer or they can be designed accordingly.

The second part of the above object is achieved by a press tool according to claim 3. This not only has the advantage of an insertion option for a preformed spacer layer while securing the same against displacement during pressing with the cover layers (which can be produced in the pressing tool, for example, by the winding method). Rather, the simplest measures (characterized in subclaim 4) ensure that there is no displacement of fiber strands into the joints between the upper and lower cheek parts when the pressing tool is closed. This ensures precise spring production in the dimensions required.

• Fig. 1 den Mittenabschnitt einer Blattfeder,
• Fig. 2 bis 5 Verfahrensschritte bei der Fertigung einer Blattfeder gemäß Fig. 1, in Querschnittsdarstellung sämtlicher Teile.

The invention is further explained below using an exemplary embodiment. The drawing shows in

• 1 shows the central section of a leaf spring,
• Fig. 2 to 5 process steps in the manufacture of a leaf spring according to FIG. 1, in a cross-sectional view of all parts.

The curved leaf spring shown in Fig. 1 with a decreasing thickness from the center to both ends is a laminated body made of fiber composite material. Here, two cover layers 1, 2 of glass or similar fiber strands embedded in a resin or similar binding compound are connected in unidirectional fiber orientation over the entire length of the spring by an interposed spacer layer 3, which is composed of a fiber fabric or scrim, for example of the same material, but with a crosswise orientation of the fibers with respect to the unidirectional fiber strands of the cover layers 1, 2 or with respect to the longitudinal axis of the leaf spring. In contrast, for example, in the fiber layers of the spacer layer 3 shown, the fiber orientation is ± 45 °. Since the spacer layer 3 should be able to absorb transverse and unilateral longitudinal forces, which lead to embrasure pressures in the bores 4 of spring connection lugs 3.1 of the spacer layer, it is of course also possible for fiber orientations to alternate ± 45 ", 0" in a special application for this purpose. / 90 "± 45" etc. can be used or also in the case of fiber fabrics +60 ". -60 °, 0", 0 °, -60 ", + 60 ° depending on the load.

This spacer layer 3 is decisive for the spring thickness decreasing towards both ends of the spring, which is achieved, for example, by layering the fabric layers with different lengths. The selected shape of the leaf spring or its spacer layer 3 has the advantage that approximately the same bending stresses over the spring length can be expected under spring deflection.

For the connection of this leaf spring, for example via a fitting on a spring support, the spring provided in the middle can Bores 4 can also be designed open in the special application. So that unidirectional fiber strands are not severed by such connection bores created in the finished spring body only, i.e. the cover layers 1, 2 are not weakened, the bores 4 are limited to the uncovered areas of the spacer layer 3, which at the two longitudinal edges of the spring from the cover layers 1, 2 in Protrude the shape of the spring connection tabs 3.1. Due to the selected arrangement of the bores 4 exclusively in the intermediate layer optimized for this purpose, high forces occurring in the transverse or longitudinal direction of the spring can be transferred to the spring connection area. This is e.g. B. indispensable in motor vehicle construction, since the leaf spring must also take over wheel guiding forces.

Of course, a leaf spring of the type described above, namely with side tabs 3.1, is not restricted to a spacer layer 3 of decreasing thickness.

• Gemäß Fig. 2 werden zunächst zur Bildung der unteren Deckschicht 2 der Blattfeder auf der Grundplatte 6.1 der Matrize 6 die beiden Wangenunterteile 7.2 positioniert unter loser Zwischenfügung von Distanzstücken 8. Die Distanzstücke 8 haben jeweils eine solche Dicke, daß der durch den Matrizenstempel 6.2 und die Wangenunterteile 7.2 begrenzte Formraum bis zu der für die Abstandsschicht 3 bestimmten Auflagerfläche 7.2.1 am einzelnen Wangenunterteil eine solche Höhe aufweist, die zumindest der Dicke der unteren Deckschicht 2 einschließlich eines für das Pressen nötigen Materialzuschlages entspricht. Andernfalls würde es, bei der dargestellten nötigen Materialdicke, beim Einbringen der unidirektionalen Faserstränge für die untere Deckschicht 2 einer entsprechenden - in dem Maße praktisch nicht realisierbaren - Präzision der angewendeten Fasereinbringmethode bedürfen, damit beim Schließen des Preßwerkzeuges über die vorgenannten Auflagerflächen 7.2.1 hinaus aus dem Formraum keinerlei Faserstränge und Bindungsmasse derselben in die Fuge zwischen den Wangenober- und Wangenunterteilen 7.1 bzw. 7.2 fließen kann.
• Gemäß Fig. 3 wird nach dem Einbringen der Faserstränge der unteren Deckschicht 2 die Abstandsschicht 3 aufgebracht, vorzugsweise als bereits gepreßter, formbeständiger Körper, der allerdings noch nicht ausgehärtet ist. Hiernach werden die beiden Wangenoberteile 7.1 positioniert. Die letzte Materialeinbringungsphase betrifft dann gemäß Fig. 4 die unidirektionalen Faserstränge der oberen Deckschicht 1 der Blattfeder. Schließlich wird das Preßwerkzeug durch Aufsetzen der Patrize 5 geschlossen. Die betreffende Fig. 5 zeigt, daß erst mit dem Schließen des Preßwerkzeuges die Distanzstücke 8 entfernt werden. Das anschließende Pressen durch Bewegen der Patrize 5 und Matrize 6 in den durch die Pfeile 9, 10 angegebenen Druckrichtungen kann in einer hydraulischen Presse erfolgen unter gleichzeitiger Zufuhr der für das gemeinsame Aushärten sämtlicher Schichten 1, 2, 3 nötigen Wärme. Es versteht sich, daß es hierbei nicht unbedingt zu einem Zusammenpressen der unidirektionalen Faserstränge um die Dicke der infolge der Distanzstücke 8 zwangsläufig zwischen der Matrize 6 und Patrize 5 einerseits und den Seitenwangen 7 andererseits vorhandenen Spalte 11 kommen muß, also diese bzw. die Distanzstücke ohne weiteres eine größere Dicke haben können, als der Preßschwund erfordert.

For the manufacture of this leaf spring, a pressing tool is preferred, in which, according to FIG. 5, a male 5 and a female 6 are each in the form of a plunger 5.2 or 6.2 seated on a base plate 5.1 or 6.1, which is provided on its two side flanks by side cheeks 7 is performed; these limit the width of the leaf spring or its layers 1, 2, 3. By profiling the side cheeks 7 as longitudinally divided versions of the spring connection tabs 3.1 with a cheek top and a cheek bottom 7.1 or 7.2 is achieved that on the one hand the spring Spacer layer 3 is secured against slipping after the pressing tool has been closed and that, on the other hand, the problem-free production process described below is only possible in the first place:

• 2, the two lower cheek parts 7.2 are positioned with the loose interposition of spacers 8 to form the lower cover layer 2 of the leaf spring on the base plate 6.1 of the die 6. The spacers 8 each have a thickness such that the through the die stamp 6.2 and the Cheek lower parts 7.2 limited mold space up to the support surface 7.2.1 intended for the spacer layer 3 on the individual lower cheek part has a height which corresponds at least to the thickness of the lower cover layer 2 including a material surcharge required for the pressing. Otherwise, with the necessary material thickness shown, when introducing the unidirectional fiber strands for the lower cover layer 2, a corresponding - to an extent practically not feasible - precision of the fiber insertion method used would be required, so that when closing the pressing tool beyond the abovementioned support surfaces 7.2.1 no fiber strands and binding mass of the same can flow into the joint between the upper and lower cheek parts 7.1 and 7.2.
• 3, after the introduction of the fiber strands of the lower cover layer 2, the spacer layer 3 is applied, preferably as an already pressed, dimensionally stable body which, however, has not yet hardened. The two upper cheek parts 7.1 are then positioned. According to FIG. 4, the last material introduction phase then relates to the unidirectional fiber strands of the upper cover layer 1 of the leaf spring. Finally, the pressing tool is closed by fitting the male 5. The relevant Fig. 5 shows that the spacers 8 are removed only when the pressing tool is closed. The subsequent pressing by moving the male 5 and female 6 in the pressure directions indicated by the arrows 9, 10 can take place in a hydraulic press with simultaneous supply of the heat necessary for the common hardening of all layers 1, 2, 3. It goes without saying that this does not necessarily mean that the unidirectional fiber strands have to be compressed by the thickness of the gaps 11 that are inevitably present between the die 6 and the patrix 5 on the one hand and the side cheeks 7 on the other hand due to the spacers 8, that is to say these or the spacers without can also have a greater thickness than the shrinkage required.

Claims (4)

1. A bending spring made from fibre-reinforced plastics material, more especially in the form of a curved leaf spring with a thickness which decreases from the centre towards both ends, in which fibre strands, in unidirectional fibre orientation over the spring length, form two surface layers (1, 2) of an intermediate layer (3) which is interpolated therebetween and is materially connected thereto and which consists of fibre fabric or the like, characterized in that the intermediate layer (3) juts out on both longitudinal edges of the spring from the surface layers (1, 2) in the form of a spring connection strap (3.1) and in that as compared with the fibre strands of the surface layers (1, 2) the fibres of the intermediate layer (3) are arranged in a predominantly crosswise orientation.

2. A bending spring according to claim 1, characterized in that spring connection bores (4) are restricted to the two spring connection straps (3.1).

3. A pressing tool consisting of upper die (5) and bottom die (6) for producing a bending spring according to claim 1, characterized in that the upper die (5) and bottom die (6) is in each case designed in the form of a die (5.2 or 6.2 respectively) seated on a base plate (5. 1 or 6.1 respectively), in which respect each die is guided at its two side flanks by side cheeks (7) which limit the surface and intermediate layer width and which are profiled in each case as longitudinally-split frames of the spring connection straps (3.1) with a cheek upper and a cheek lower part (7.1 or 7.2 respectively).

4. A pressing tool according to claim 3, characterized in that between the base plate (6.1) of the bottom die (6) and the cheek lower parts (7.2) are loosely inserted distance pieces (8) of at least such a thickness that a moulding chamber bounded by the female die (6.2) and the cheek lower parts (7.2) has, as far as a bearing surface (7.2.1) on the individual cheek lower part intended for the intermediate layer (3), a height which corresponds at least to the thickness of the lower surface layer (2) including a material increase necessary for the pressing.

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